The Penman-Monteith method with a variable canopy resistance using hourly weather data was evaluate to estimate evapotranspiration (ETPM) over a tomato canopy at the Panguilemo Experimental Station located in Talca (VIIth Region of Chile). A variable canopy and aerodynamic resistances for the tomato canopy were included in the Penman-Monteith equation. Data collected included air temperature, air vapor pressure, wind speed, incoming solar radiation, net radiation, net radiation soil heat flux, latent heat flux and stomatal resistance.
The performance of the Penman-Monteith method was evaluated using evapotranspiration measured by the Bowen ratio energy balance method (ETB). Results indicated that there was a good agreement between ETPM and ETB with an overall standard error of estimate of 60 W/m2 and absolute relative error of 10%.